Circuit for use in musical instruments



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United States Patent O 3,006,228 CIRCUIT FOR USE IN MUSICAL INSTRUMENTS James Paul White, 6711 Charles St., Philadelphia, Pa. Filed Nov. 14, 1957, Ser. No. 696,404 17 Claims. (Cl. 84-1.01)

This invention relates to certain novel circuit arrangements which may be used to produce a pleasing musical eifect. More specifically, the present invention relates to a musical instrument which uses gates or switch circuits to produce tones rich in overtones or quality. The invention further relates to an instrument which may be easily played even by one unskilled in musical techniques.

The present invention is intended to provide a simple circu-it arrangement, using circuits for the most part well understood in the art, to produce a more colorful quality tone for use in electronic musical instruments of various types. 'I'he quality is attained by using a part of the original input signal as the generating source. This same signal may be used with frequency dividers to produce musical tones in a variety of octave ranges other than the original. Moreover, the quality may be adjusted and controlled by means of a simple shaping circuit which merely selects or modifies different portions of the original input signal to produce different musical eifects.

The present invention is directed in particular to the use of gate circuits to produce the desired quality improvements. A gate circuit is a circuit having both signal input and control input terminals, which circuit is so arranged that the nature lof the voltage applied to the control input terminals at any insta-nt is elfective to control the transmismission to the output terminals of the voltage applied to the signal input terminals of the device. The voltage applied to the control input terminals of a gate circuit may be derived from a-frequency divider similar to those presently used in many types lof electronic organs, of which the device described in U.S. Patent 2,486,039 to N. Langer is an example. If, under these conditions, a voltage having a fundamental frequency which is an integral multiple of the fundamental frequency at which the divider is operat ing is applied to the signal input terminal of the gate, then a signal having the same fundamental frequency as that at which the frequency divider is operating, but having an amplitude controlled only by the signal input to the gate, will appear at the output terminals of the gate. The gate then functions as a signal frequency divider under the control lof the frequency divider itself, but in such a way that none, or ya negligibly small portion, of the output of the frequency divider is transmitted to the output of the gate circuit. [In other words, signals applied to the control input terminals of the gate cannot be transmitted to the output terminals of the gate, but are only effective in controlling the transmission through the gate of signals applied to the signal input terminals of the gate. Hence, this system of controlling the output wave produces an output which is wholly derived from the input signal, and is generally proportional to the prime input signal in amplitude as well as in frequency. This relationship remains true regardless of how many gate circuits the signal passes through before reaching the final output terminals of any possible system of gate circuits.

A variety of musical instruments are possible using the circuitry of the present invention. It is possible to use tones produced by keyboard instruments in some known and conventional manner, for example, and by means of the simple circuitry of this invention obtain more beautifor example, a simple tune whistled by the operator into 3,006,228 Patented Oct. 31, 1961 an input microphone of an instrument in accordance with the present invention may be transformed into an output much richer and more pleasing than the input signal. The circuitry is by comparison with known equipment for the same purpose so simple as to bring the cost of electronic musical instruments into a range in which such instruments will be more generally available to the public. Moreover, because of the ease of their operation, such instruments may well create greater interest in the playing of musical instruments.

More specifically, in its simplest form my invention consists of a circuit for use in ya musical instrument. This circuit has a pulse generator which is responsive to an original input signal and which is adapted to generate a pulse at a frequency corresponding to that of the input signal. At least one frequency divider is provided to respond to the pulse to produce a square wave having a period equal to some integral power of two times the period of the original input wave. The output of the frequency divider is applied to control terminals and the input signal is applied to the input terminals of a gate circuit which is constructed so that a ixed portion of the original input signal is passed once each full cycle of the signal output from the frequency divider.

The original frequency can be enhanced in a modified version of the invention using a pulse of that frequency at the control as well as input terminals. The basic circuit arrangement described is also modified and made more versatile by the addition of further frequency dividers to provide various octave tonal ranges from which to select an output. Even with additional frequency dividers, a single circuit of this type will produce only one letter note at a time, perhaps at several octaves, but multiple circuit arrangements will permit a number of diiferent letter notes to be played simultaneously with enriched tone and enhanced quality.

Other modifications will be clear from a discussion of particular embodiments of my invention shown in the accompanying drawings in which:

FIG. l is a block diagram showing schematically a circuit which is used in connection with a monophonic instrument of the present invention;

FIGS. 2a to 2p are wave forms which appear in different parts of Ithe circuit of FIG. l all on- -the same time axis;

FIGS. 3a through 3c are circuit diagrams parts of a circuit suitable for use in accordance with the system shown in FIG. 1;

FIG. 4 is a modified circuit arrangement which may be substituted for part of the circuit shown in FIG. 3b; and

FIG. Sis a schematic arrangement similar to FIG. l but showing the circuit elements necessary to use of the present invention in an instrument in which a number of notes are simultaneously reproduced.

Referring rst to FIG. 1 and FIGS. 2a and 2p the monophonic instrument of -the present invention will first be considered using the block diagram of FIG. l to describe broadly the various functional parts of the device, and how they coact. FIGS. 2a-.2p will aid in the understanding of the functioning of the instrument of FIG. 1. In this connection it should be observed that FIGS. 2a to 2k represent wave forms which may occur in different parts of the device of FIG. l, and FIGS. 2l to 2p are intended. to represent modifications which may be accomplished in the wave shaping circuits.

Referring to FIG. l, musical tones originate at a source 10 which may be a phonograph record with a suitable pickup or a microphone picking up a whistled tune, 'or some other manner of picking up musical tones. For the successful use of the monophonic instrument, the tones should be single notes as opposed to chords, successive ones of which, however, may vary sequentially in pitch. The tone produced at source may be represented by the wave form shown in FIG. 2a, and if whistled, will probably be close to the pure sine wave shown although Waves of other shape may be successfully used. The amplifier 1'1 enlarges in amplitude the wave form of FIG. 2a to produce the wave form of FIG. 2b. This amplified wave is then fed to pulse generator 12 which produces one pulse each cycle. The pulse may be in the form of a square wave, such as is illustrated in FIG. 2c, or may be in the form of a narrow peak pulse occurring 'once each cycle. The pulse, however, should be in some form useful to generate square waves at the following frequency divider. The pulse fed into the frequency divider 13 will produce an output square wave, such as that shown in FIG. 2d, in which the period of the square wave is twice the period of the original wave of FIG. 2a as well as those of FIGS. 2b andv 2c, or half the frequency of those waves. The wave of FIG. 2d may be fed to the control terminals of a first gate 14, and the input signal shown at FIG. 2b may 'be fed directly from the amplifier 11 to the signal input terminals of gate 14. The gate 14 functions to control the amount of signal which appears at the output terminals, allowing only a controlled amount through. Thus the wave form of FIG. 2g may appear at terminal 15 of octave range switch 16 from the output terminals of the gate. It will be observed that in accordance with the control function exercised by gate 14 a full cycle of the input signal wave is permitted to pass once each cycle of square wave of FIG. 2d. Moreover, the portion of the wave is so selected that the wave generated has a discontinuity at its beginning and at its end. Since the wave of FIG. 2g is not a sine wave, but involves complex wave form, yet having the basic qualities derived from the original signal of FIG. 2a amplified, the result of this process is production of wave of FIG. 2g, a wave -forrn rich in overtones cornpared with the input wave. As is appreciated by those skilled in music, the quality of music is dependent upon the amount and kind of overtone present. Thus it will appear that a simple sine wave input, such as is created by whistling, may be turned into a highly pleasing musical tone having the wave shape as shown in FIG. 2g.

If it is desirable to make the same note available in dierent octave ranges, additional frequency dividers 17, 18 and 19 may be provided. Frequency divider 17 receives the output signal from frequency divider 13 and produces a square waveof the form shown at FIG.. 2e. Frequency divider 18 produces a square wave of the form shown in FIG. 2f, from the output of frequency divider 17, etc. The output of frequency divider 17 is fed to the control terminals of gate 20 which has signal input terminals which may be fed from the output terminals of gate 14 through an isolating amplifier 21. At the output terminals of gate 20 the signal shown in FIG. 2h is produced. Since isolating kamplifier 21 effectively'in- 'verts this signal from the sense of the signal of FIG. 2g, an inverting amplifier 22 may be employed to o'btain the wave form of FIG. 2k which is applied at terminal 23 of octave range switch 16. The output signal obtained at Ythe output terminals of gate f24 has twice the period of the wave of FIG. 2h. Since it passes through isolating amplifier 25 before reaching gate 24, no inverting amplifier is required because isolating amplifier- 25 has already reinverted signal of FIG. 2h.V Hence the output of gate A24 is shown in FIG. 2]'. Other gates 26 used with other frequency dividers 19 and other isolating amplifiers 27, as required, tendv to produce signals in the same way, successive gates producing signals of lower and lower octaves. Isolating amplifiers 27 may or may not be used between the stages, but if used, will make desirable the use of inverting amplifiers at the output terminals of even gates for the purpose of reinversion of the signal used. The outputs of the various gates are fed to the octave switch 16 and give a selection of the pitch of the output.

by simply changing the position of the octave range switch, which may conveniently be done manually by the operator.

The basic qualities of the wave are retained in a relatively small section of the wave, especially in lower octaves. For some purposes the tone quality of the wave as generated is most desirable. In other situations other types of waves are desired. Wave shapes, such as shown in FIGS. 2m through 2p, are possible to obtain with simple circuitry in wave shaping circuits 30. The output from the wave shaping circuit may then be passed through 'tone control circuits 31, gain control arrangement 32, suitable amplifier means 33 to the speaker output 34.

It should be emphasized that the signal from the source need not be sinusoidal in wave form. It is simply necessary that the harmonic content be limited to the extent that there are no more than two points of zero voltage during each period of the input wave. This limitation is imposed by the nature of the frequency divider circuits and is a necessary requirement for the frequency dividers to function properly.

It should also be noticed that in the operation of the pulse generator 12 the phase of the input signal is shifted by an angle of somewhat less than and then the phaseshifted signal is converted into a wave form which is approximately square. As previously mentioned, however, it need not be square and may be some other form of pulsed wave in which a pulse occurs once each cycle. In the arrangement described, it is the negative going portion of the wave of FIG. 2c, for example, which causes the first frequency divider 13 to change state so that its polarity -will be reversed on the output leads. The following negative going portion of the wave will return the output of the frequency divider to the original state, to complete one cycle, thus accomplishing frequency division.

The inversion of the `wave of FIG. 2h to the wave of FIG. 2k would not be audible to the ear. However, it is necessary to invert this wave in order to allow the wave shaping circuits to act upon the signal carry portion of each wave form which reaches it in the same way.

FIGS. 3a-3c show a practical circuit which accomplishes the effect ascribed to the more schematic arrangement of FIG. l. The component circuits are for the most part known to those skilled in the art and will therefore be treated in some cases rather summarily. The circuit is divided into three figures which are shown in this way for the purpose of making detail sufficiently clear to be easly understood. FIG. 3a shows the source, the amplifier, and the pulse generator portions of the system of FIG. 1. FIG. 3b shows the frequency dividers, the gates, the isolating amplifiers and inverting amplifiers. FIG. 3c shows the octave range switch, the wave shaping circuits, tone control circuits, the gain control, the amplifier and output terminals to which a suitable power amplifier and speaker may be connected.

As shown in 3a the source 10' may be a microphone. The amplifier 11 may be of any conventional type including a three stage resistance-capacitance coupled amplifier, as shown. The amplifier may contain a gain control 40 in the form of a potentiometer to adjust the amplification to suit various conditions, as required. The output of the amplifier is then fed through a cathode follower 41 to an output lead 42. Lead 42 branches one branch going to the circuit portion shown in FIG. 3b and another part to a phase shifting circuit consisting of a resistor 43 and capacitor44. Phase shifting is required to prevent the input signal as amplified, FIG. 2b, from being in phase with the output of the pulse generator so that the frequency dividers will not change state to open and/ or close the gates when the signal is passing through zero or-nearly zero. Instead the phase shift which occurs due to network 43-44 causes the gates to open and close when the signal is near or at its maximum so that as aresultthe signal hasan'abrupt rise and fall of voltage associated with the opening and closing of the gates. As is well known to those familiar with wave form analysis, a wave having a steep wave front is much richer in content than a wave having no such rapid rise or fall in voltage. For this reason it is highly desirable that the gates open and close when the amplified input wave of FIG. 2b is in the vicinity of its most extreme maximum or minimum excursion. In practice the actual phase shift produced is normally selected so that it is in the neighborhood of 80. However, it will be clear to those skilled in the art that, by a proper selection of the values of resistor 43 and capacitor 44 the phase shift may be adjusted as desired in order to produce somewhat different harmonic effects.

The pulse generator 12 is illustrated in FIG. 3a as an overdriven amplifier having resistance-capacitance coupled amplifier stages using simple triodes. The resistors 45 and 46 at the output of the pulse generator form a voltage divider to provide the correct amplitude of the pulse at the output lead 47. Another type of pulse generator could, of course, be substituted for the one shown in FIG. 3a.

Referring to FIG. 3b, the output signal from the pulse generator is fed on lead 47 to the input terminals of frequency divider 13. Frequency divider 13 like frequency dividers 17 and 18 is shown as an Eccles-Jordan flip-flop circuit. In accordance with normal operation capacitors 48 and 49 couple the grids of triodes 51 and 52, respectively, to the input circuit. Since frequency dividers 17 and 18 are essentially like frequency divider 13, their components have been given the same designators. The effect of the capacitors 48 and 49 is to differentiate the signal fed into the frequency divider and thereby provide positive and negative pulses on the grids of tubes 51 and 52 in the regions of rapid change of state of the input square wave. Negative pulses are produced by the negative-going portions of the input square wave while positive pulses are produced by the positive-going portions of the input wave. In connection with frequency divider 13, for example, the square wave of FIG. 2c fed into the frequency divider circuit will produce output on lead S3 corresponding to the wave shape shown in FIG. 2d. A change of state of this ip-op circuit is initiated by the negative pulses as can be seen from comparison of the wave forms of FIGS. 2c-2f. The output from triode 52 is fed to frequency divider 17 along lead 53. The output from triode 51 is fed through lead 54 to the control terminals of gate 14. The output of frequency divider 17 is arranged to be fed through lead 55 to frequency divider 18 which, as shown, is the last frequency divider, although additional -frequency dividers may be provided as indicated by the dashed line box 19 and its associated boxes in FIG. l. The output of frequency divider 17 is also fed through lead 56 to gate 20, and the output of frequency divider 18 is fed only through lead 57 to gate 24. The signal from amplifier 11 (FIG. 3a) is fed from its output terminal through lead 42 to the signal input terminal of gate 14.

The signals fed to leads 54, 56 and 57, respectively, from the frequency dividers are rfed to the control terminals of gates 14, 20 and 24 through a network similarly identified in each case and consisting of resistors 63 and 64 and capacitor 65. The gates 14, 20 and 24 are shunt type double triode switch circuits similar except for the grid biasing arrangement to those shown in the book entitled Wave Forms by B. Chance et al., on page 377 in FIG. 10.13. The triodes 69 and 70 as illustrated have a `common grid connection but have their electrode arrangements reversed although they are arranged in what would otherwise be a parallel circuit between the ground and the signal input and output terminals. It will be observed that, when the square wave applied to the grids of triodes 69 and 70 is in its most positive state, the grids of the triodes are slightlyv positive with respect to ground. Under these conditions the triode 69 will provide a low impedance between its cathode and plate with respect to negative signals on its cathode, and triode 70 will provide a low impedance between its plate and cathode with respect to positive signals on its plate. On the oth-er hand, when the signal applied to the grids is in its least positive state, the grids of triodes 69 and 70 will be negative with respect to ground, and hence both triodes will be cut off. Under these conditions, the path through these triodes from the cathode of triode 69 or the plate of triode 70 to ground will be open-circuited, in effect.

In operation of the gate 14, for example, the resistor 71 in lead 42 and the resistance on the signal output lead 73 through the triodes 69 and 70 to ground constitute a voltage divider. When the signal input supply through lead 42 passes through resistor 71, it will appear on the output lead 73 with only slightly diminished amplitude if the triodes 69 and 70 are in their high resistant state. However, if the triodes are in their low resistant state, practically all of the signal will appear across the resistor 71 and almost none of the signal will appear across the tubes 69 and 70. Since these two conditions repeat, on lead 73 a wave form such as that shown in FIG. 2g will be generated.

The resistance capacitance network made up of resistors 63 and 64 and capacitor 65 connected as shown to the grids of the respective gates function in the operation of the gate circuit. Thus, since the lead' 54, from the frequency divider 13, for example, and the corresponding lead from the other frequency dividers, is always positive with respect to ground, if the lead were connected directly to the grids for the triodes 69 and 70 through a simple resistor, it would be impossible 'to drive the grids of these triodes negative with respect to ground. Capacitor 65 in parallel with resistor 64 overcomes this diiculty by charging when lead 54 is most positive. During charging, the plate of capacitor 65 that is connected to the grids of the triodes 69 and 70 is possibly at -ground potential. The other plate is charging positively. When the potential on the lead 54 falls to its least positive value, the capacitor 65 will start to discharge through the resistor 64. However, as the capacitor 65 starts to discharge, the voltage it applies to the grids of the triodes 69 and 70 will be negative, and sufciently greater in magnitude than the magnitude of the voltage on lead' 54, to cause the grids of triodes 69 and 70 to become negative and prevent current flow between their electrodes. Under these conditions, practically no current ows through resistor 63, and the potential at the junction point of resistors 63 and 64 is practically the same as at the output terminal the frequency divider 13. If, for example, this potential were plus volts, and the capacitor 65 were charged to volts with the plate connected to the grids of the triodes negative, then the potential on the grids would be 25 volts negative, and the triodes 69 and 70 would be cut olf. When the potential at the output of the frequency divider rose to plus 175 volts, for example, more than 50 volts would be available to attempt to drive the grids positive, and the triodes 69 and 70 would have returned to their low resistance state. Resistor 63 is used to limit the charging current of capacitor 65 and prevent overloading of the frequency divider 13.

Gates 20 and 24 which include triodes similarly designated operate in the same manner yas does gate 14. Resistors 73 and 74 cooper-ate with triodes of gates 20 and 24, respectively, in the same manner in which resistor 71 worked with the triodes of gate 14. Since the period of the output voltage wave on lead 54 of frequency divider 13 is one-half and one-quarter of the periods on leads 56 and 57, respectively, their capacitors 65 will have to be appropriately selected to charge and discharge to the same voltage levels, but at one-half and one-quarter times the rate of charge and discharge of the capacitor between frequency divider 13 and gate 14.

Amplifiers 21 and 25 are used for isolation, and amplifier 22 is used for inversion discussed in connection with FIGS. 1 and 2. Voltage `dividers consisting of resistors 78 and 79, resistors 80 and 81, resistors 82 and 83 serve to determine the voltage output of the three amplified tubes. The signal from gate 14 is fed via resistor 78 to the triode 85 of amplifier 21, the output of which passes through blocking capacitor 86 to resistor 73' and to the signal input terminals of gate 20. The signal from gate 20 is fed via resistors 80-81 to tube 87 of amplifier 25, the output of which p-asses through a blocking capacitor 88 and resistor 74 to the signal input terminals of gate 24 and lead 89. The signal from gate 24 is taken from conductor 89. The signal from gate 20 is also fed via resistor 82 to tube 91 of amplifier 22 the output of which passes through a blocking capacitor 92 and resistor 93 to output conductor 94. The signal from gate 14 is taken from conductor 72.

Referring now to FIG. 3c, the leads 72, 94 and 89 carrying the signals output of gates 14, 20 and' 24, respectively, are brought into the octave range switch 16 which has a plurality of terminals for each of these leads, each capable 4of carrying signals representing corresponding pitches in different octave ranges, and a selector contact arm to selectively connect the output from one of the gates to the balance of the circuitry. When the moving arm of octave range switch 16 is on position 15, the signal appearing on the output conductor 96 will have a fundamental frequency one-half that of the input signal of FIG. 2a as -may be seen from FIG. 2g; when the moving arm of switch 16 is on position 97 or 98, the signal on conductor 96 will have a fundamental frequency one-quarter or one-eighth, respectively, of that of the input signal as may be seen in FIGS. 2k and 2j, respectively. 'I'he signal on conductor 96 passes through resistor 100 and blocking condenser 101 to the grid of cathode follower tube 102. From the cathode of tube 102 the signal passes through blocking capacitor 103 to a lead connected to -a terminal 104 of switch 105. This signal will be essentially the same as the signal which appears on lead 96 when capacitor 121 is unused (as shown). The wave shape which is repeated to form the signal over a period of time is shown in FIG. 21. Negative signals fed from capacitor 103, however, may also pass through rectifier 107 to a lead which connects to terminal 108 of switch 105. The rectifier 107 acts to remove the positive portions of the signal and leaves the wave of FIG. 2m. Signals from the output of rectifier 107 may also `be applied to a differentiating circuit composed of capacitor 108 and resistor 109. The differentiated signal appearing across resistor 109 is amplifiedby vacuum tube 110 and cathode follower tube 111, and passes through blocking condenser 112 to a lead which connects to position 113 of switch 105. The signal wave form at terminal 113 is shown at FIG. 2n. Positive signals at terminal 113, however, may also pass through rectifier 114 to terminal 115 of switch 105. In this event, the rectier 114 removes the negative portions of the signal and leaves the wave shown in FIG. 2p. Cathode follower tubes 102 and 111 are used to provide a low impedance source for rectifiers 107 and 114 respectively. yAmplifier-tube 110 is used to restore the signal level which has been reduced by the use of the `differentiating circuit composed of capacitor 108 and resistor 109. Hence, all of the four possible signal wave forms which may appear at the output of switch 105 will have comparable amplitudes, and no gain readjustment will be necessary when switch 105 is turned through its severalV positions. Switch 120, which is ganged to switch 105, has similar switch positions. Its function is to add capacitor 121 to the circuit whenever switch 105 is on terminals 113 or 115. Capacitor 121 and resistor 100 form a filter network, the function of which is to compensate for the amplitud'e vs. frequency characteristic of differentiating circuit 108-109 on the varying frequencies of the various scale tones in a musical selection. If filter 121 were not used, when the switch 105 is connected to terminal 113 or 115, then the amplitude of the signal at the output of switch would be much greater at the high end of the musical scale than at the low end because of the fact that capacitor 108 passes the high frequency tones more readily than the low frequency tones. This would make the audible signal much louder in the treble than in the bass range. To overcome this effect filter 100--121 is used to attenuate the higher -pitched signals more than the lower pitched ones, and

so restore the balance in volume between the treble and bass tones. Filter 100- 121 will have negligible effect on the four wave forms appearing at switch 105. The wave forms of FIGS. 2l and 2m will be unaffected because when switch 105 is in position to pass either of them, switch will have a position which disconnects the capacitor 121 from the circuit. When the wave form of either of FIGS. 2n or 2p is selected by moving switch 105 to terminals 113 or 115, capacitor 121 is connected into the circuit by switch 120. Under these conditions, capacitor 121 will act as an integrating device as desired and selectively reduce the amplitude of the signal fed to tub'e 102; however, since input to the wave shaping circuits may be of a shape shown in any of FIGS. 2g, 2k or 2]', it is obvious that this wave is not -a pure sine wave, but contains numerous harmonics which will be attenuated more by capacitor 12.1 than will the fundamental frequency. The higher |the harmonic, the more it will be attenuated. However, it is well known to those skilled in the art that the higher harmonies are represented in a wave form by the portions of the wave containing abrupt discontinuities. These discontinuities are concentrated at those points where the Wave rises abruptly from zero voltage, or descends abruptly to zero voltage. Hence, the wave form feeding tube 102 under these circumstances will be similar to one of the waves shown in FIGS. 2g, 2k or 2]' except that their positive portions will be distorted much more than the negative portions because it is the positive portions which contain the bulk of the higher harmonics. When this distorted wave passes through rectifier 107, the positive portions of the wave are removed and the harmonic content of the wave appearing in the subsequent circuits will be negligibly different from that which would have appeared had capacitor 121 not been used. The desired result of reducing the amplitude of the fundamental and all harmonics of the upper scale tones will, however, have been achieved. Thus the waves of FIGS. 2n and 2p will have their scalewise amplitudes equalized by capacitor 121, but will be unaffected in their wave forms.

Switch 105 is used to select one of the wave forms appearing at terminals 104, 108, 113, and 115 and routes the signal through the capacitor 118 to the tone control circuits 31 and specifically to the grid of cathode follower tube 125. Cathode follower tube 125 feeds a three section adjustable low-pass filter consisting of variable resistors 126 and capacitors 127. The output of this filter feeds cathode follower 129 which feeds an adjustable high-pass filter consisting of capacitor 131 and variable resistor 132. The output of this filter feeds cathode follower tube 133 which feeds potentiometer gain control 32.

The output of gain control 32 through terminal 135 feeds subsequent circuits which may further amplify 'the signal and deliver it t-o a loudspeaker for translation into audible sound.

As has been said, the operation of the monophonic musical instrument describedcan be accomplished merely by whistling into the microphone. Since whistling has little musical appeal because of its poor timber due to its lack of overtones, it is subjectto a great deal of improvement in quality. A secondl weakness in a whistled tone is that it is in a frequency'range higher than that employed by almost all non-electrical musical instruments. Whistling has the advantage, however, of being perhaps the most simple and easily controlled method by which persons untrained in music are able to produce a melody. Since the device of the present invention will be seen to overcome the irst two disadvantages and to produce a sound rich in harmonics within a pleasing frequency range simply by whistling, it should have great appeal to persons untrained in music but who are nevertheless able to carry a melody. Moreover, use of the instrument should require only a few hours of practice to produce music having a tonal beauty even liner than that which can be obtained within any existing electronic instruments on which a non-accompanied melody is played. It furthermore can be used as a solo instrument or played with suitable accompaniment. In fact, the soloist himself is able to accompany himself on some sort of manually operated instrument if desired. For example, the player of `an electronic organ which may, or may not, itself be made in accordance with the prese-nt invention can also use the monophonic instrument which may, or may not, as desired, employ the organ speaker for its sound output. It will be necessary in each application of the monophonic instrument to avoid a feedback by providing adequate separation between the microphone into which the player whistles and the speaker from which the sound emanates, but this requirement is not diicult to meet since only one of the many harmonies present in the output of the speaker will coineide in frequency with the note being whistled into the microphone. tActual tests show that it is possible to raise the output volume to such -a level that the person playing the instrument is conscious that he is whistling only as he hears the ultimate effect of the whistling in the signal produced by the loud-speaker. This effect, in turn, leaves the player with the impression that he has a very responsive and powerful instrument at his command.

Although there have been monophonic instruments inv the prior art such as shown and described in U.S. Patent No. 2,514,490 to J. M. Hanert, the use of gate circuits to produce an entirely new effect constitutes an important advance. Moreover, instruments of the type previously known were limited in number of possible pitches which they could produce, which pitches were ordinarily those of the tempered scale or twelve no-tes of fixed vibration in each octave. As a consequence, rthe output frequency in such instruments has not always been in exact proportion to the input frequency produced by the performer by whistling, singing, humming, or otherwise. In the present invention, by contrast, the performer is able to maintain control over the pitch of the output at all times. This exact control over the pitch has a number of advantages which may be summarized as follows: (a) True portamento is possible; (b) The vibrato produced by the performer is not lost but is present in the output; (c) The natural unsteadiness characteristic of many instruments will not be lost, and, when not overdone will serve to prevent any possible mechanical quality in the output tones; (d) It is possible to depart from the tempered intonation as desired and play a note either higher or lower in pitch than the usual tempered pitch, thus an instrument constructed in accordance with this invention could be used to harmonize perfectly with an a-cappella choir; (e) The present invention can harmonize with any instrument regardless of whether the instrument is tuned to a standard pitch, such as' an A -at 440 vibrations per second, or not.`

As pointed out in the previous description, the various circuits making up the whole instrument are for the most part well known as standard circuits for which there are many known equivalents. In most instances equivalents will not be suggested since they are so well known in the art. However, in the case of the gate circuit, an equivalent is shown in FIG. 4'since the use 10 of the gate circuit is a necessary device to produce the ends of the present invention.

FIG. 4 shows a modified portion of the circuit of FIG. 3b, showing particularly an alternative gate circuit which may be substituted for the one in FIG. 3b. The output from the frequency divider 13 is fed viaconductors 54 and 53', respectively, to resistors 150 and 151, Iand thence to twin diodes 152 and 153. This type of gate circuit is known as a four-diode shunt bidirectional switch. In the case of this alternate gate, it is necessary to provide control signals balanced with respect to ground rather than the one conductor 54 unbalanced yarrangement of FIG. 3b. To provide control signals balanced with respect to ground it is necessary to provide a separate power supply for the frequency dividers and to have it isolated from ground. This supply is indicated in FIG. 4 as Supply #2, where the only connection between this supply and that powering the rest of the device is through capacitor 154 which insures that the two supplies shall be at the same A.\C. potential. When lead 54 is more positive than lead 53', current will ow through all four diodes of tubes 152 and 153. This will provide a low impedance between conductor 156 and conductor 157, which is at ground, through diodes 152 and 153. This will prevent the input signal of FIG. 2b from causing an appreciable voltage to be built up on conductor 156 becafuse of the large voltage drop that will occur in resistor 158. However, when lead 54 is more negative than lead 53', diodes of tubes 152 and 153 will be biased in their reverse direction and current will be unable to ow through them. Under these conditions these diodes will present a very high impedance from lead :156 to ground (lead 157) and almost all of the signal of FIG. 2b will appear on lead 156, since there will be only a slightly voltage drop in resistor 158. Capacitors 159 and 160 might be added as shown, if it were desired to have the current ow in diodes of tubes 152 and 153 start and stop more rapidly. The circuits to which the signal appearing on lead 156 is `fed are the same as those in FIG. 3b.

In general, it will be seen that the action of the diodes of tubes 152 and 153 is quite similar to those of the gate triodes 69 and 70 of FIG. 3b in that each shunts the signal to ground periodically in response to the control signals from the frequency dividers. There is another class of circuits which may perform the same switching function by opening the lead carrying the signal, and so disconnecting it from the output circuits. Either of these types of gating circuits, commonly known as either the shunt switch or the series switch, may be conveniently used as gating circuits in the musical instruments of the present invention. A number of these switch circuits are described in Wave Forms by Chance, et al., Sec. 10.3, pages, 370-381. Others are shown in article in the Bell System Technical Journal, April 1939, page 318. Various other circuits have appeared in the Proceedings of the IRE: December 1949, page 1474; August 1949, page 855; July 1952, page 797; January 1955, page 29. All of these types of circuits could conceivably be used, although the ones shown may have certain advantages such as efficiency or simplicity. An article describing the use of magnetic devices as gates may be seen in the September 1954 issue of Electronics, page 174, Saturable Transformers as Gates, by B. Moffat.

Throughout this entire specification, the words electric, electrical or electronic musical instruments shall be understood to refer to all possible musical devices which could perfonm the function described, and which make use of electricity, either in whole or in part, to produce the desired eifect. Such devices could therefore be electronic or magnetic in nature, or could be any other type of solid state device which would produce equivalent results. Possible examples of such devices would be the transistor, the magnetic amplifier or magnetic switch, and the crystal diode. Although the present disclosure does not specically show all of these devices, it is apparent 1 1 that those skilled in the art could readily apply any of these means to produce the same or equivalent results.

Although the present invention has been disclosed in connection with certain preferred embodiments thereof, it will be apparent to those skilled in the ait that many modifications and variations thereof may be made without departing from the fundament-a1 principles of the invention. Moreover', the circuit arrangements described fmay be used in many types of musical instruments other than monophonic instruments to achieve fine tonal quality with a relatively simple arrangement. For example, in almost all of the instruments commonly known as electric or electronic organs, a master volume control, usually operated by the foot, and known as an expression control, is provided to enable the player to adjust the output volume of the organ to any desired value. The gate circuits of the present invention provide an alternate way of performing the same function, in organs which utilize the master oscillator frequency divider principle to generate musical tones having the same letter name throughout the instrument.

An example of the gate system of the present invention applied to an electric organ, for example, or some other type of electronic musical instrument other than a monophonic instrument, is shown in FIG. 5. tFig. is also intended to show the minimum equipment required in accordance with the present invention, so that amplifiers, etc., are eliminated. 'Component circuits corresponding to parts of the system of FIG. l are shown by similar designators, with the addition of primes thereto. It will be noted, however, that in addition to corresponding terminals on the octave switch 16 a terminal 170 is provided for connecting the signal input directly to the output through switch 170. Additionally, it will be noted that the arrangement is such that the same note in more than one octave may be selected, as a situation in which a chord is played having two notes of the same scale number.

It will be appreciated that the device when applied to a conventional musical instrument will be applied in such a way that the iixed notes of a tempered scale, for example, will be treated. Moreover, to be sure that sutiicient number of systems, each capable of producing one letter note, are available, `at least as many systems and octave range switches 16a, 16b, etc. (connected if desired to the same output) will have to be supplied as the maximum number of notes which can be played at one time. Since this is the case, and since the tempered scale is used in most instances, it will probably be deemed desirable to use twelve systems, one for each note of the tempered scale, each system being essentially the same as that shown connected to octave range 16' and being connected through its own octave range switch 16a16b etc. Then for ex ample, as any note on a keyboard is pressed, generating a tone, that particular letter tone in any octave will be taken care of by the same system in accordance with the present invention, and every other tone of another letter designation will be taken care of by separate system.

FIG. 5 also shows that the outputs of the successive gates need not be used to feed the next gate, but instead each gate may be fed directly at its signal input terminals from the original signal input as represented in FIG. 2a or 2b. The path taken in this event is shown schematically by the dashed line passing beneath the gates to the input terminals of all gates after the rst.

FIG. 5 also shows that it is possible to use the signal input frequency generated by the pulse generator, particularly if it is a square wave, in connection with a gate 172 of its own. It will be immediately appreciated that this arrangement is not without difliculty since less than one cycle of the input wave will have to be used, and if a characteristic portion of a wave is selected to Iaccurately reproduce vthe tone it may be difficult to select that portion of the wave such that it is passed by the gate at a point of maximum `or minimum voltage and cut olf at a similar point. Nevertheless, the possibility of such use is within the scope of the applicants invention.

The use of gate circuits in a musical instrument is believed to be a novel application of the gate circuit, and to produce very significant advantages over other types of frequency dividing circuits, of which U.S. Patent No. 2,486,039 to N. Langer is an example. The outstanding difference between the previous art and the present invention resides in the fact that the previous art makes use of a waveform derived from the frequency divider as the output signal of the frequency divider in question. In other words, a voltage wave produced by the frequency divider is transmitted from the divider to the subsequent amplifying timbre control, and output circuits for ultimate conversion into musical sound. My invention, however, does not make use of the wave form of the frequency divider as an output signal from the frequency divider. In this invention the voltage wave that is transmitted to the subsequent circuits is always a gated version of the original signal, as previously described. When a gate circuit is used it is definitely undesirable to transmit to the subsequent circuits any of the energy produced by the frequency divider itself. The amount of energy that is so transmitted is negligible, and can theoretically be reduced to zero by proper balancing of the gate circuits. In brief, the frequency dividers of the previous art are used to generate tone signal wave forms at the frequency in question, whereas the frequency dividers of the present invention are used for the purpose of providing voltages for application to the control input terminals of gate circuits, through which gates the signal itself is periodically allowed to pass on to the subsequent circuits.

I claim:

l. A musical instrument tone quality circuit comprising a pulse generator responsively coupled to an original input signal applied across its input terminals for generating across its output terminals pulses at fundamental frequency corresponding to that of the original input signal, at least one frequency divider having its input terminals coupled to the output terminals of the pulse generator for producing across its output terminals a square wave having a period equal to two raised to some integer power times the period of the original input sig nal, and a gate circuit having input, control and output terminals the input signal being applied to said input terminals, having a portion of which corresponds approximately to the original input signal, and the output terminals of the frequency divider are coupled to the control terminals a portion of the original input signal passing to the output terminals of the gate once each full cycle of the signal output from the frequency divider.

2. A musical instrument tone quality control circuit comprising a pulse generator having input and output terminals, responsively coupled at its input terminals to an original input signal for generating at its output terminals a square wave at a fundamental frequency corresponding to that of the original input signal, and a gate circuit having input, control, and output terminals, the original input signal being received at its input terminals, its control terminals being connected to the output of the pulse generator, and its output terminals receiving a fixed portion of the original input signal passed once each full cycle of the pulse generator square wave.

3. The circuit of claim l in which no more than one cycle of the original input signal is passed each period of the square wave from the frequency divider.

4. The circuit of claim 3 in which the frequency divider produces a square wave output signal having a period of two raised to some integer power times the period of the original input signal.

5. The circuit of claim 3 in which a wave shaping circuit is provided for quality control of the output.

6. The circuit of claim 4 in which at least one more frequency divider is coupled at its input terminals to the output terminals of the preceding frequency divider, each successive frequency divider serving to produce an output square wave of double the period or half the frequency of its input square wave and in which frequency controlled gates are provided for each of the frequency dividers, the output terminals of each frequency divider providing the control signal for ya. corresponding gate to permit an output signal containing no more than one cycle of the original input signal no more than once each period of the control signal across its output terminals.

7. The circuit of claim 6` in which the signal input terminals of successive lower frequency controlled gates are fed from `the output of the next previous higher frequency gates.

8. The circuit of claim 6 in which the signal input terminals of all gates are fed by the original input signal.

9. The circuit of claim 6 in which an octave selector switch is coupled to the output terminals of each gate to select the output from any one of the gates.

10. The 'circuit of claim 6v in which a wave shaping circuit is coupled to the output gate terminals for quality control of the output.

11. The circuit of claim in which the wave shaping circuit is adapted to 'select a portion of the output of the gate or pass the whole gate output and in which the wave form of the output of the gate may be changed, said circuit including compensating circuit elements adapted to preserve the amplitude of the output of the gate.

12. A musical instrument in accordance with claim 9 in which a plurality of circuits responsive to separate signal sources are employed 'and in which the output from the various octave range switches is fed to a common output device.

13. A monophonic musical instrument comprising an input signal transducer for creating `an original input signal, a pulse generator having input and output terminals, responsive at its input terminals to the original input signal and generating pulses at its output terminals at a fundamental frequency corresponding to that of the original input signal, at least one frequency' divider having input terminals coupled to said output terminals 'of the pulse generator for producing at its output terminals a square wave having a period equal to two raised to some integer power times the period of the original input signal applied to its input terminals, a signal frequency dividing gate circuit for each frequency divider having control term-inals coupled to each frequency divider and input terminals to which an -input signal having 14. The rn-onophonic instrument of claim 13 in which l the input signal is produced from an 'audible 4tone by the input signal transducer.

15. The monophonic instrument of claim 14 in which there are a plurality of successive frequency dividers with their input terminals connected to the output terminals of the previous frequency divider such that the first doubles the period of the generator produced pulse and each successive divider doubles the period of its predecessors square wave signal, in which the output termin-als of each frequency divider are coupled to the control terminals of a signal frequency dividing gate which permits an output signal containing no more than one cycle of the original signal no more than once each period of the control signal, and in which an octave selector switch is provided to selectively couple the various output terminals of the gates to the output circuits.

16. The monophonic instrument of claim 15 in which the pulse generator produces la square wave of the input frequency and in which the cont-rol terminals of a gate are coupled to the output of the pulse generator and the origin-al signal is applied to its input terminals.

17. The monophonic instrument of claim 15 in which a wave shaping circuit is adapted to alternatively select different portions of the output and modify the wave form without destroying the effective amplitude of the output signal.

References Cited in the tile of this patent UNITED STATES PATENTS 2,126,682 Hammond Aug. 9, 1938 2,201,160 Curtis May 21, 1940 2,560,600 Schafer July 17, 1951 2,634,052 Bloch Apr. 7, 1953 2,672,553 Dickinson- Mar. 16, 1954 2,738,463 Metzger Mar. 13, 1956 2,752,593 Downs June 26, 1956 2,764,679 Berkowitz Sept. 25, 1956 2,766,379 Pugsley Oct. 9, 1956 2,816,959 Segerstrom etal. Dec. 17, 1957 2,834,011 Mork May 6, 1958 

